Umbro Soccer

I think to have a jersey West Brom because they are on sale and the only size they have is a small or XL.
I do not know the size of the cards UMBRO, but here are my dimensions:
I'm 6'4
My size is 34
I weigh 157 pounds.

I do not think so. I wore Umbro kits before and they tend to adapt, like any other brands. However, the trend these days (at least in terms of professional teams) is facing a tight fitting shirt. So I guess what I'm saying is, even if L is normally a little big for you, you should be OK.